Emerson E2 Manuel D’Utilisation

The refrigerant temperature is subtracted from the 

value of an ambient air temperature sensor. The result is 
the temperature differential. It is this differential value 
that is compared to the PID setpoint for the purpose of 
determining the amount of total fan capacity to activate.

In an evaporative condenser, water is sprayed across a 

condenser coil, which cools the refrigerant as water is 
evaporated. Control of the evaporative condenser is simi-
lar in ways to the air cooled strategy in that the Condenser 
Control application uses PID control to activate or deacti-
vate fans (thus increasing or decreasing the amount of 
evaporative cooling).

Like air-cooled condensers, evaporative condensers 

may be controlled by discharge pressure or temperature. 
They may also be controlled by water sump temperature. 
In addition, each evaporative condenser may have up to 16 
“override” sensors (either temperature or pressure) that 
allow the condenser to be overridden to fast recovery 
mode (See Section 11.2.5, Fast Recovery).

Condenser Control applications can control three dif-

ferent kinds of fans: single-speed fans (up to 12 stages), 
two-speed fans, and variable-speed fans. All fan types are 
controlled by PID control; in other words, the Condenser 
Control application generates a percentage from 0% to 
100% that corresponds to the amount of total fan power 
that should be active. 

Single-speed fans translate the PID percentage into a 

percentage of total fan capacity. For example, if the PID 
percentage is 75%, then 75% of all condenser fan stages 
will be ON.

Two-speed fans use Cut In/Cut Out setpoints to trans-

late the percentage into an OFF, LO, or HI fan state. 

Variable-speed fans simply use the percentage to 

determine the fan speed. Thus, a 51% PID percentage will 
result in the fan running at 51% maximum speed.

VS-SS combined fan setup is for the combination of a 

variable-speed fan with single-speed fans. First, under PID 
control, the variable-speed (VS) fan turns on. Then as the 
PID percentage rises above VS fan’s maximum speed, the 
E2 switches on additional single-speed fan stages.

The E2 is capable of operating condensers in a special 

mode that reduces its condensing capacity. This special 
mode is called split mode.

Split mode is most often used in cold climates during 

periods of low outside air temperature. Split mode is also 
sometimes used when heated refrigerant from the refriger-

ation system is being used as reclaim heat by an HVAC 
unit.

The most common way E2 achieves split mode in an 

air-cooled condenser with single-speed fans is to lock OFF 
50% of the total number of fans. You may choose to lock 
OFF all odd-numbered fans, even-numbered fans, the first 
half of all fans, or the last half of all fans.

Split mode can also be achieved by activating a valve 

that bypasses a portion of the tubing in the condenser man-
ifold. The resulting decrease in surface area results in 
reduced cooling.

Under certain conditions the system pressure may 

increase too quickly above the condenser setpoint to be 
reduced effectively by normal condenser control. The E2 
provides a user-definable fast recovery rate setpoint at 
which all the condenser fans are turned ON to reduce sys-
tem pressure.

For air-cooled and temperature-differential condenser 

strategies, discharge pressure is always used as the control 
value that determines fast recovery. You may choose to 
enable or disable fast recovery, and also to include a delay 
when transitioning from one mode to the other.

For evaporative condensers, up to 16 “override” tem-

perature sensors may be combined to yield a single over-
ride value that is used for fast recovery. Fast Recovery is 
always used in an evaporative condenser.

An overview of the input and output devices that make 

up a typical Condenser Control application is shown by 
Figure 11-2 and Figure 11-3. Figure 11-2 shows the typi-
cal layout of an air-cooled condenser. Figure 11-3 shows 
the typical layout of an evaporative condenser.